Integral shield for reducing capacities



Dec. 20, 1949 N. J. RElTZ ETAL 2,491,932

INTEGRAL SHIELD FOR REDUCING CAPACITIES Filed Oct. 8, 1946 INVENTORS; I lEi 2 I George l/J/aomis 4; Norman JReitz Th e [r Hii'arney Patented Dec. 20, 1949 INTEGRALSHIELD FOR REDUCING: CAPACITIES Norman .J. Reitz' and George L. Loomis, Em- I porium, Pa., assignors to Sylvania Electric Products, Inc.,a corporation of Massachusetts Application October 8, 1946, Serial No. 701,934

4 Claims. (Cl. 250-275) This invention relates to electron discharge devices and has for its primary object the reduction of the capacities among the electrodes due to the end effects of those electrodes. A further object is to reduce the input capacity of amplifier tubes having an end spacer of mica or the like, and to reduce the input capacity tolerance Of tubes of any given type.

Radio tubes and the like devices currently in usepincludea cathode, an anode, optionally one or-more grids. and at the ends of t ese electrodes which are generally parallel there are spacers ordinarily of mica for fixing the mutual position of the electrodes. It is desirable to reduce to a minimum the interelectrode capacities due to end effects of the electrodes without intefering with functional portions thereof. According to one prior art suggestion, a grounded shield surrounding the anode is provided, supporting a pair of inwardly extending plates at one end of the tube, which plates are bowed downwardly into contact with the mica spacer. The purpose of the downward extension is to shield the anode from the grid support rods that commonly extend through the mica. This structural feature is advantageous in reducing the plate-to-grid interelectrode capacity.

Apparently there has been no appreciation of the need and the feasibility of reducing the electrostatic coupling between the ends of multiple electrodes within the thickness of the spacer, through structural modification of the spacer and through particular shielding construction.

Accordingly a furt er object of the invention is to reduce the interelectrode capacity of electron dischar e devices having an end spacer of mica or the like. and to reduce the input capacity tolerance of tubes of a given type, A still further obiect is to reduce the plate-to-grid capacity of electron discharge devices of the tvpes which include an end spacer and a control grid.

A specific embodiment of the invention is disclosed below, which will promote an understanding of the principles of the invention, and of certain further objects and features thereof.

upper portion of the Shielding cage in Figs. 1 and 2 before assembly to the other elements; and

Fig. 4 is a lateral view partly in section of a complete vacuum tube incorporating an electrostatic shield such as is shown in the other figures. In Fig. 1 the elements of the tube mount are 2 shown, including two-part anode 10, multiple grids. l2, l4, and I6, and cathode l8. The sections of the anode are connected by straps H. Each of the grids has a pair of lateral supporting rods 20 which extend through spacer 22.

The prior art in one instance has sought to reduce the interelectrode capacity due to end structure of the electrodes, where a mica spacer was used,v by providing lateral extensions from an electrostatic cage or shield 24 surrounding the tube mount. It is that construction which has been selected as being peculiarly well adapted to modification in accordance with the present invention. 'In the drawings, the prior art lateral extensions 26 and 28 of electrostatic shield 24 are shown with axial extensions 30 and 32 bearing on the end mica, to shield the ends of rods 20' from anode i0. It is to be understood that certain aspects of the invention are entirely independent of that type of shielding cage.

In conformity with the broad purpose of the present invention, the end spacer of mica or other material, is slotted to break into the direct lines of electrostatic coupling primarily between the ends of the control grid and the anode. Axial sheet-metal portions 34 and 36 are struck out of extensions 26 and 28 as shown in Fig. 3. Portions 34 and 36 project through apertures 38 provided in spacers 22 and are positioned relatively close to the anode.

The effect of the electrostatic shielding portions which extend through apertures in the mica spacer is to reduce the stray capacity due to the relatively high dielectric constant of the spacer. Irrespective Of this consideration, the novel shielding extensions operate to reduce the end-effect in a region where the various grids do not function as they do near the center region, remote from their ends. The helical grid wires terminate short of the end spacers. The fact that the novel shields are positioned quite close to the anode insures interruption of the curvilinear electrostatic paths from one grid, for example, the control grid to the anode and bypassing another grid, the screen grid. for example. In one specific type of amplifier tube employing the shielding cage and rod-end shields, a ten percent reduction in the control-grid-toanode capacity was effected by inclusion of shields 34 and 35.

The above embodiment discloses the electrostatic shield as extending through the upper spacer. It will be understood that shields of this character may also be arranged to extend through the lower spacer (not shown). Furthermore, the axial shields 34 and 36 may be of other than the flat shape shown, where anodes of other shapes are employed. In the described embodiment there are two fiat anode sections. Hence it is necessary merely to avoid the end effects which rest on the outside surface of said spacer and project through said spacer between the spaced parts of said anode and said grid.

,4. An electron discharge device including an anode, a cathode, and a grid, a fiat end spacer fixing the mutual orientation of said anode, said vgrid. and said cathode, said anode having porsurface of said spacer, and additional: extensions of said shield projecting through said spacer between the end portionsv of said anode and said grid,

2; An electron discharge device-according to claim 1 including an additional grid between said anode and said named grid, said-additional extensions penetrating said spacer between said anode and said additional grid.

3 An electron discharge device including an anode, a cathode, and a grid,'a flat end spacer fixing the mutual orientation of said anode, said grid and said cathode, said anode having portions cut away at oneend whereby only spaced parts of said anode contact said spacer, an electro-static shield external of said anode,jand lateral extensions on said shield having portions tions cut away at one end whereby only spaced parts of said anode contact said spacer, an

" electro-static shield external of said anode, lateral extensions on said shield having portions which rest: on the outside surface of said spacer, said means including an elongated slot in said spacer and additional extensions of said shield projecting through said slot.

NORMAN J. REITZ. GEORGE L. LOOMIS.

REFERENCES CITED The following, references are of, record the file of. this patent:

UNITED STATES PATENTS Number Name Date 2,087 ,327 McNally July 20, 193'! 2,154,141 Wheller Apr. 11,1939 2,167,885 Glans Aug. 1, 1939 2,250,184 Miller July 22,1194! 

